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Strawberries better preserved thanks to a bioactive film

New biofilm for the preservation of strawberries

A major breakthrough in the field of packaging. Mrs. Monique Lacroix, professor at the French National Institute for Scientific Research (INRS), has developed, with her team, a film that can extend the shelf life of strawberries, a fruit well known to be fragile, for up to 12 days, and protect them against mold and certain pathogenic bacteria. 

This new innovative film is made of a natural molecule called chitosan. It is obtained by degrading chitin, a polymer derived from the shell of crustaceans. The film also contains essential oils and silver nanoparticles which both have antimicrobial properties. “Chitin is what makes the shell rigid,” explains Mrs. Lacroix, professor and researcher at the INRS food research labs (LABO-RESALA) and the Canadian Irradiation Center (CIC). “When this product is degraded, chitosan is obtained, a polymer that is more flexible and more soluble as well.

Chitin degradation products also have antimicrobial properties that vary depending on the size of the molecules. They are known primarily for their antifungal properties. They inhibit mold quite easily; hence the interest in using them for fruit and vegetables. It is even believed that they could be used for the preservation of cheeses.”

Monique Lacroix added that the essential oil vapors of the film protect the strawberries by having a synergetic effect with the nanoparticles, thereby extending the preservation time. When the film is in contact with the fruit, the chitosan and nanoparticles prevent the development of mold and pathogenic bacteria on the surface. The research team has tested its packaging film on 4 different microbial cultures: Escherichia coli (E. coli), Listeria monocytogenes (Listeria), Salmonella Typhimurium (Salmonella), and Aspergillus niger, a very resistant mold that causes a lot of losses in strawberries. Finally, thanks to its composition, the film is also biodegradable. If it is buried, it will be degraded by the bacteria found in the soil.”

As a byproduct of food, chitin has many uses. Monique Lacroix mentioned that in the Philippines, chitin is degraded even further in order to make monomers that are then used to activate plant growth, including sugar plants. Chitosan is also used in the medical field. It is used in materials for various applications such as the controlled release of drugs, for example. 

Monique Lacroix is not new to the research in new packaging films. Her first works go back to the 1990s. She had then developed films from dairy proteins and byproducts of the cheese industry. At the time, she had shown that when this polymer is irradiated in the absence of oxygen, it is possible to make packaging films that are fully insoluble in water.

“And that is very important when marketing a biodegradable film for food products. This discovery had allowed for the creation of the Bio-Envelope company.”

The bioactive film developed by Monique Lacroix and her research team at the INRS is made of chitosan, a natural molecule obtained by degrading chitin, a polymer derived from the shell of crustaceans. The film also contains essential oils and silver nanoparticles which both have antimicrobial properties. 

Monique Lacroix mentioned the big challenges in creating new packaging films: they must be water-resistant, oxygen permeable, capable of letting carbon dioxide through so the fruit does not ferment and soften, and they must have the right mechanical properties to be resistant.

“That is why it takes such a long time before fully biodegradable films made from natural products can appear on the market.”

In their study, Monique Lacroix and her team used the bioactive packaging film on strawberries and then irradiated it. “And we obtained synergies between the two. After 12 days, 50% of the strawberries that had not been packaged with our film and had not been irradiated were moldy. This percentage dropped to 38% for the products packaged with the film made of chitosan, essential oils, and silver nanoparticles. And with added irradiation, the loss was reduced to 20%.”

When released on the market, the new film is expected to be sold at a slightly higher price than other packaging films currently available. Monique Lacroix adds that over time, this price will go down, as it has for products made with polylactic acid, a polymer produced by fermentation and used to make yogurt containers and shampoo bottles.

“Initially, these products were very costly to produce. But we have developed technologies to reduce those costs. We must therefore move forward, look at what can be done, develop the films, and then work as a team with experts from the industry to try to reduce the production costs.”

When will the new revolutionary film be launched on the market? Not just yet, apparently. The INRS professor explained that at the moment, there is a lack of partnerships with packaging manufacturers. Several are waiting to see what products will be developed before investing.

“It is important to work in collaboration with manufacturers, in order to use their production methods of course, but also to adapt the technologies to move forward.”


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